Stellar dynamics in CH Ind and SW CMa disprove need for circumbinary planets

Star system: SW CMa | Distance from the Sun: 1890 light years

Eclipsing binary stars—systems where two stars periodically pass in front of each other from our perspective—often show small shifts in their orbital timings. These shifts, known as apsidal motion, are sometimes used to search for third objects like planets orbiting both stars. This study evaluates two such systems, CH Ind and SW CMa, to determine if their observed orbital changes truly indicate the presence of external planets or if they are simply the result of natural stellar behaviors.

By using precise measurements of the stars' masses and sizes from previous studies, the research team calculated the expected gravitational interactions between the two stars themselves. These internal stellar effects, such as tidal forces where gravity distorts the shape of the stars, can mimic the orbital patterns that might otherwise be mistaken for the gravitational pull of a circumbinary planet.

For both systems, the calculated movement caused by the stars themselves aligns closely with the actual observed data. In the case of SW CMa, the inclusion of accurate star dimensions increased the expected classical stellar contribution by sixteen times, bringing the theoretical prediction into agreement with observations. Consequently, neither system provides evidence of an extra planet affecting their orbits.

Key findings
- CH Ind and SW CMa show no evidence of circumbinary planets.
- Orbital timing shifts in these systems are fully explained by the stars' internal physics.
- Standard bulk searches for planets can misinterpret natural stellar tidal forces as third-body signals.
- Accurate, system-specific stellar models are essential before claiming planet discovery in binary systems.

Scientific study

Stellar tidal systematics in apsidal-motion searches for circumbinary planets: CH Ind and SW CMa (external link)